[1] Harvard Med Sch, Gastrointestinal Unit, Massachusetts Gen Hosp, Boston, MA 02115 USA
[2] Karolinska Inst, Dept Med Epidemiol & Biostat, Stockholm, Sweden
[3] Harvard Med Sch, Massachusetts Gen Hosp, Clin & Translat Epidemiol Unit, Mongan Inst, Boston, MA 02115 USA
[4] Univ Utah, Sch Med, Div Gastroenterol Hepatol & Nutr, Salt Lake City, UT USA
[5] Uppsala Univ, Dept Surg Sci, Uppsala, Sweden
[6] Karolinska Inst, Div Clin Epidemiol, Dept Med Solna, Stockholm, Sweden
[7] Karolinska Inst, Dept Clin Sci & Educ Sodersjukhuset, Stockholm, Sweden
[8] Orebro Univ Hosp, Dept Paediat, Orebro, Sweden